The direction of propagation of light emitted by a point source having a hemispherical radiation pattern is controlled to produce a desired light distribution pattern. Particularly, through the use of refraction and internal reflection, an optical element alters the light emission pattern of, for example, a light emitting diode to produce an illumination pattern dictated by the intended use of the device into which the light emitting diode is incorporated.
While not limited thereto in its utility, the novel technology to be described below is particularly well suited for use in combination with light emitting diodes (LED's) and, especially, for use in warning and signaling lights.
Commercially available LED's have characteristic spatial radiation patterns with respect to an optical axis which passes through the light emitting die. These radiation patterns, which are primarily determined by an integral lens, include “Batwing”, “Lambertian” and “Side Emission”. A common characteristic of all of these radiation patterns is that there is emission in a pattern surrounding the optical axis from one side of a plane containing the light emitting die, the optical axis being oriented perpendicular to this plane. The light generated by an LED is radiated within a hemisphere centered on the optical axis. The distribution of light radiation within this hemisphere is determined by the shape and optical properties of the lens (if any) covering the light emitting die of the LED. Thus, LED's can be described as “directional” light sources, since all of the light they generate is emitted from one side of the device.
When designing light sources for a particular purpose, it is important to maximize efficiency by ensuring that substantially all of the generated light is arranged in a pattern or field of illumination dictated by the end use of the device into which the light source is incorporated. The somewhat limited overall light output of individual LEDs frequently necessitates that several discrete devices be cooperatively employed to meet a particular photometric requirement. Use of arrays of LEDs and their directional emission pattern present peculiar challenges to the designer of warning and signaling lights. Employing LEDs in compact arrays additionally imposes cooling, i.e., “heat sinking”, requirements which were not present in the case of prior art warning and signal light design.